Status of Key Insect Pests in Desert Produce and Melons
Last fall, pest pressure in the desert was historically low for some pests, while unusually heavy for other pests. Through September, insect pressure has been all over the board. Some pests like beet armyworm have been heavy, and other like whiteflies have been uncharacteristically light. Of course, the Yuma growing area is quite large and pest populations can vary according to location. Here’s how I see it so far this season.
Beet armyworm/Cabbage looper/Corn earworm: Last fall was a pretty average worm year in produce. This fall, beet armyworm pressure has been exceptionally heavy in some areas (Dome Valley, Yuma Valley). They also appeared a bit earlier than normal. For instance, a review of trials here at YAC over the past 10 years has shown that larvae typically show up about 10 -11 days after wet date. This year, I observed larvae on lettuce at 8-9 days and had several reports from PCAs of them consistently showing up at 6-7 days on cotyledons and 1 true leaf stage lettuce. They appeared to slow down a bit in the past week or so. With cooler weather in the immediate forecast, armyworm pressure should decrease. Corn earworm appeared early in September, but are much lower now. Cabbage looper are starting to show up on lettuce and cole crops, as expected with cooler weather. For information on insecticides available for Lep management see Lep Control Chart, 2018.
Diamondback moth: To date, DBM have been very light. An occasional report of light larval populations on transplants in Roll and Dome Valley, but no control issues reported. DBM larvae have been almost non-existent on plots at YAC, as opposed to last fall when DBM larval population on direct-seed broccoli were higher than what we normally see; a result of migration. However, nothing comparable to the fall of 2016. Trap catches have overall been lighter compared with last season, but moth numbers increased this past week (see DBM Trap Network). It will be interesting to see if we observe an increase in trap captures following Hurricane Rosa’s track through Northern Baja California and Sonora. DBM have been shown to move long distances in storms.
Bagrada bug: The pest has been almost non-existent the last three years, and this fall doesn’t appear to be any different. There have been a few reports of adults showing up, but numbers have been light and feeding damage negligible. Chemigation of pyrethroids have been effective.
Whitefly/CYSDV: Areawide, whiteflies in fall melons have been at very low levels relative to years past. Whitefly adult numbers on sticky traps placed next to melon crops have been very light so far; lighter than last year in most areas. Accordingly, CYSDV infection is also very light in all fields from Texas Hill to Dome Valley. Virus symptoms (yellow interveinal chlorosis) are patchy, and mainly on the edges of fields suggesting PCAs and growers are doing a great job of preventing secondary infection. Areawide, whiteflies were similarly light in produce crops with an occasional flare-up in some isolated areas. Trap catches are down with the exception of locations near recently defoliated cotton (see Areawide Trap Network).
This study was conducted at the Yuma Valley Agricultural Center. The soil was a silty clay loam (7-56-37 sand-silt-clay, pH 7.2, O.M. 0.7%). Spinach ‘Revere’ was seeded, then sprinkler-irrigated to germinate seed Jan 18, 2024 on beds with 84 in. between bed centers and containing 30 lines of seed per bed. All irrigation water was supplied by sprinkler irrigation. Treatments were replicated four times in a randomized complete block design. Replicate plots consisted of 15 ft lengths of bed separated by 3 ft lengths of nontreated bed. Treatments were applied with a CO2backpack sprayer that delivered 50 gal/acre at 40 psi to flat-fan nozzles.
Month
Max
Min
Average
Rainfall
January
68
42
54
1.14 in
February
73
47
59
0.50 in
March
77
50
63
0.31 in
Downy mildew (caused by Peronospora farinosa f. sp. spinaciae) was first observed in plots on Feb 19 and final reading was taken on February 26, 2024. Spray date for each treatments are listed in excel file with the results. Disease severity was recorded by determining the percentage of infected leaves present within three 1-ft2 areas within each of the four replicate plots per treatment. The number of spinach leaves in a 1-ft2 area of bed was approximately 144.
The data (found in the accompanying Excel file) illustrate the degree of disease reduction obtained by applications of the various tested fungicides. Products that provided effective control against the disease include Orondis ultra, Thrive 4 M, Fungout, Cevya, Eject and Zampro. No phytotoxicity was observed in any of the treatments in this trial.
Controlling Disease and Weeds with Band-Steam – Yuma Trials Show Good Promise
In previous articles (Vol. 11 (13), Vol. 11 (20), Vol. 11(24)), I’ve discussed using band-steam to control plant diseases and weeds. Band-steaming is where steam is used to heat narrow strips of soil to temperature levels sufficient to kill soilborne pathogens and weed seed (>140 °F for > 20 minutes). The concept is showing good promise. This past season, three trials were conducted examining the efficacy of using steam for disease and weed control in Yuma, AZ. In the studies, steam was applied in a 4-inch-wide by 2-inch-deep band of soil centered on the seedline using a prototype band-steam applicator (Fig.1). The band-steam applicator is principally comprised of a 35 BHP steam generator mounted on top of an elongated bed shaper. The apparatus applies steam via shank injection and from cone shaped ports on top of the bed shaper.
Trial results were very encouraging as the prototype applicator was able to raise soil temperatures to target levels (140°F for >20 minutes) at viable travels speeds of 0.75 mph. Steam provided better than 80% weed control and significantly lowered hand weeding time by more than 2 hours per acre (Table 1). Results also showed that Fusarium colony forming units (CFU) were reduced from 2,600 in the control to 155 in the 0.75 mph and 53 in the 0.5 mph treatments, respectively (a more than 15-fold reduction). A significant difference in Fusarium wilt of lettuce disease incidence was not found, however disease infection at the field site was low (< 2%) and differences were not expected. At 0.5 mph, fuel costs were calculated to be $238/acre which was considered reasonable and consistent with the values reported by Fennimore et al. (2014).
An unexpected finding was that plants in steam treated plots appeared to be healthier and more vigorous than untreated plots (Fig. 2). This trial is still in progress and it will be interesting to see if this improved early growth translates into increases in crop yield.
In summary, early trial results are showing good promise for use of band-steam as a non-herbicidal method of pest control. We plan on conducting further trials in this multi-year study. If you are interested in evaluating the device on your farm and being part of the study please contact me. We are particularly interested in fields with a known history of Fusarium wilt of lettuce and/or Sclerotinia lettuce drop that will be planted to iceberg or romaine lettuce.
As always, if you are interested in seeing the machine operate or would like more information, please feel free to contact me.
Acknowledgements
This work is supported by Crop Protection and Pest Management grant no. 2017-70006-27273/project accession no. 1014065 from the USDA National Institute of Food and Agriculture, the Arizona Specialty Crop Block Grant Program and the Arizona Iceberg Lettuce Research Council. We greatly appreciate their support. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
A special thank you is extended to Mellon Farms for allowing us to conduct this research on their farm.
References
Fennimore, S.A., Martin, F.N., Miller, T.C., Broome, J.C., Dorn, N. and Greene, I. 2014. Evaluation of a mobile steam applicator for soil disinfestation in California strawberry. HortScience 49(12):1542-1549.
Click link below or picture to see the band-steam and co-product applicator in action!
Carryover of Vegetable Herbicides to Wheat Grown in Rotation
Almost all the herbicides used on lettuce, cole crops and melons have restrictions on how soon wheat can be planted in rotation after they have been used. Experience has demonstrated, however, that safe intervals can vary considerably based upon many factors and are almost always much longer than they need to be. The most important factors are rate applied, irrigation practices and tillage. For example, when Kerb used to be banded at 2 to 4 lbs. per acre after planting and incorporated with furrow irrigation, it was common to see treated strips across wheat fields which followed. This is uncommon now that lower rates are Chemigated. We still see some Balan injury at ends of fields or in overlaps especially when sudan is planted. Wheat it not very sensitive to Prefar and carryover injury is uncommon.
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
